1. Field of the Invention
The present invention generally relates to a belt tightener for a seat belt for use with passengers in moving vehicles, such as cars, trucks, roller coasters, etc. More particularly, the present invention relates to a belt tightener for tightening a seat belt when the vehicle is subject to sudden deceleration.
2. Related Art
A pre-loader device is designed to quickly tighten a seat belt to eliminate any slack therein and protect the passenger in conjunction with the locking of the retractor. To enable the seat belt to be tightened in a short time, conventional devices have been proposed that cause the seat belt buckle to move using spring force of a torsion bar or a coil spring. Such a tightening device is disclosed in, e.g., Japanese Unexamined Patent Publication Nos. 4-63746 and 61-241234. Another proposal for tightening a seat belt has been to reel a seat belt using the explosive power of powder, for example. Such a device is disclosed in, e.g., Japanese Unexamined Patent No. 63-22752.
Each of the above conventional seat belt buckles is provided with a locking mechanism for locking the tongue plate of the seat belt and a release button for releasing the locking operation of the locking mechanism in order to make the seat belt detachable. However, these systems have the problem that, after the seat belt buckle is pulled in by the pre-loader during a sudden stop of the vehicle, for example, as the seat buckle has been displaced, the release button can not be quickly operated when the passenger attempts to leave the vehicle. Such a problem poses problems in the event of motor vehicle accidents.
It is desirable that the pre-loader device should be actuated to protect the passenger not only when the vehicle collides but also when the vehicle is running on a rough road, for example. However, conventional devices have been designed taking only collisions into consideration, and therefore, the whole device has to be replaced after the device is actuated a single time.
It is desirable that a pre-loader device complete the tightening of the seat belt in a short time from when sudden deceleration of the vehicle is detected to when the body load of the passenger is applied to the seat belt. However, conventional pre-loader devices are not yet actuated in a sufficiently short enough time.